The invention relates to a drive mechanism for the character wheels in a recording calculator, and more particularly to a gear drive mechanism in which a one-way rotation of drive gear is translated in turn to two idler gears to impart a bi-directional two-speed rotation to a driven gear.
Gear drives which are used to rotate the character wheels in a recording calculator are known in the prior art. Such drives must be capable of setting the character wheels to a print position, then of holding the character wheels in the print position while printing is effected, and lastly of resetting the character wheels to a rest or home position in readiness for the next printing operation. One arrangement for rotating character wheels is shown by German Pat. No. 1,122,304. In this patent, a reversal of the direction of rotation of a driven shaft is accomplished by a mechanism in which a cam controlled lever engages, by means of a gear segment, a gear which is located on a shaft which is to be driven. A reversal of rotation of a character wheel is effected by the action of a cam control on the gear segment. While this mechanism produces the character wheel motion which is desired, there are several disadvantages. Special means must be provided to maintain the shaft in a set position during the printing operation. Because the control lever experiences long travel distances during operation, considerable space is required. Also, the cam plate and the radius of action of the cam plate are design factors which prevent the utilization of small printing units. The cam plate when moving in one direction must counteract a return spring, and this counteraction results in a favoring of motion in one direction over motion in the opposite direction. This directional motion favoring results in differing ratios of forces which become more imbalanced when it is desired to have the velocity of motion in one direction be greater than the velocity of motion in the opposite direction.